The DPP is a multi center national clinical trial with the aim of preventing NIDDM. DPP will be targeted towards individuals who have impaired glucose tolerance (IGT), a condition in which blood sugar levels are higher than normal but not high nough to be diabetic. Persons who have IGT will be recruited to participate in DPP. Over half will be from the ethnic minorities at high risk of developing NIDDM. Recruitment will begin in 1996 and the study will continue until 2001. One of the treatments to be used in DPP is lifestyle intervention consisting of intensive attention to diet and exercise, a combination that is thought to ameliorate abnormal glucose metabolism. Goals are to decrease body weight by at least 7% and to increase energy expenditure by 700 kcal per week. In addition, two pharmacologic agents that improve blood glucose levels and other metabolic agnormalities associated with IGT will be used in combination with "Basic Care." Thus there will be a group receiving "basic care" plus metformin, a group receiving "basic care" plus troglitazone, and another group treated with "basic care" plus placebo. Volunteers will be randomized to the four groups and the 3 medication groups will be double blinded. Outcome measurements will include annual physical examinations, electrocardiograms, oral glucose tolerance tests, and blood tests to measure lipids and other cardiovascular risk factors.